AbbVie and Roche are looking to move key oncology drug Venclexta deeper into the blood cancer arena, but their ambitions in multiple myeloma just took a hit.

The FDA has halted enrollment in all of Venclexta's myeloma trials, the companies said Tuesday. The reason? The Venclexta arm of a phase 3 study, dubbed Bellini, turned up a higher proportion of deaths than the control arm did.

Though the partial clinical hold will keep new patients from enrolling, patients who are already participating—and benefiting from Venclexta—can continue treatment after talking things over with their doctors, AbbVie said. The development won’t affect any of Venclexta’s currently approved indications in chronic lymphocytic leukemia and acute myeloid leukema.

"We are committed to patient safety and are thoroughly analyzing the results observed in the Bellini trial. We will continue working with the FDA and worldwide regulatory agencies to determine appropriate next steps for the multiple myeloma program," Michael Severino, M.D., AbbVie’s vice chairman and president, said in a statement.

It’s not a good sign for the drugmakers, which are looking to Venclexta to pad their oncology sales before biosimilar copies damage their largest moneymakers. It won’t be long before AbbVie’s Humira—and Roche’s Herceptin, Rituxan and Avastin—go up against lower-priced rivals, and they’ll need all the help they can get from other products to make up for lost sales.

And until now, Venclexta had been going strong in trials. Last year alone, it picked up two FDA approvals: one in tandem with Roche’s Rituxan in relapsed CLL, and one in newly diagnosed AML. And late in the year, another Venclexta combo—pairing Venclexta and Roche's Gazyva—hit its marks in a phase 3 trial, too.

But the drug isn’t the first closely watched cancer treatment to run into problems in myeloma. In 2017, Merck paused enrollment on a pair of phase 3 Keytruda studies in multiple myeloma to investigate deaths among patients taking the IO star with Celgene’s Revlimid and Pomalyst.

Ultimately, the FDA put two trials on full hold and stopped dosing in a third, with all patients discontinuing treatment.